Multi-layer PCB is a circuit board that has more than two layers.

Unlike a Double-Sided PCB which only has two conductive layers of material, all multilayer PCBs must have at least three layers of conductive material which are buried in the center of the material.

How Are Multi-layer PCBs Made?

Alternating layers of prepeg and core materials are laminated together under high temperature and pressure to produce Multilayer PCBs. This process ensures that air isn’t trapped between layers, conductors are completely encapsulated by resin, and the adhesive that holds the layers together are properly melted and cured. The range of material combinations is extensive from basic epoxy glass to exotic ceramic or Teflon materials.

The figure above illustrates the stack-up of a 4-Layer/ multi-layer PCB. Prepeg and core are essentially the same material, but prepeg is not fully cured, making it more malleable than the core.The alternating layers are then placed into a lamination press. Extremely high temperatures and pressures are applied to the stack-up, causing the prepeg to “melt” and join the layers together. After cooling off, the end result is a very hard and solid multi-layer board.

Benefits of Multilayer PCBs

Higher assembly density

Smaller size (considerable savings on space)

Increased flexibility

Easier incorporation controlled impedance features

EMI shielding through careful placement of power and ground layers

Applications of Multilayer PCBs:

While the weight and space benefits of multi-layer PCBs are especially valuable for Aerospace PCBs, multi-layer PCBs are also beneficial to applications where “cross-talk” levels are critical. These are a few other the applications using multi-layer printed circuit boards: